A triac is a semiconductor device which is capable of controlling large load currents with considerable flexibility inasmuch as conduction of the anode circuit for each anode polarity, may be produced with either direct current or alternating current signals at the gate terminal. The signal may be of a relatively low current level.
This form of semiconductor device oftentimes forms a portion of the load circuit or final stage of a control circuit which may be of solid state components and whose control functions are carried out at logic power levels. In the prior art the configuration of circuit for interfacing the load circuit and the solid state control circuit has suffered from the disadvantages both of being costly and cumbersome aspects of a solid state control.